Interlocking structural members employing triple interfitting wedge

ABSTRACT

The invention relates to an expansion fastener device that secures two interlocking members together. The device includes a parallelepiped receptacle having slits along opposite ends. The receptacle is inserted through the interlocking members and triple wedges are driven into the receptacle. The triple wedges includes a first wedge having tapers in the vertical direction and its insertion into receptacle causes only vertical expansion of the receptacle. A pair of horizontally tapered wedges are inserted into the receptacle alongside the first wedge and they cause only horizontal expansion of the receptacle. Utilization of the invention reduces stress points as created by conventional rivets.

FIELD OF THE INVENTION

The present invention relates to a fastenerless joint, and moreparticularly to such a joint for composite aircraft structures.

BRIEF DESCRIPTION OF THE PRIOR ART

In many fabrication applications laminated structures are attached tosupport structures by common fastening techniques. In one particularapplication, composite laminated aircraft wing skins are attached to asupport substructure by means of rivets. Within the aircraft environmentthis creates several problems. In the first place, the rivets passingthrough the various plies of the laminated structures create stressforces which could cause rupture and ultimate destruction of theaircraft.

In modern fabrication techniques for composite aircraft skins, fuel orother liquids are often contained within the skin so that the aircraftstructure itself creates a reservoir for the fluid. A serious problemwith current construction techniques utilizing fasteners is the presenceof leaks where rivets penetrate the composite laminate.

For these and other reasons, it would be highly desirable to create amechanical joint between aircraft composite laminated skin structuresand support subassemblies without the utilization of discrete fasteners.

BRIEF DESCRIPTION OF THE INVENTION

The present invention utilizes a triple wedge assembly for mechanicallyinterlocking a composite laminate wing skin structure to a supportsubstructure.

Hollowed projections are formed in rows from the wing skin laminate andthese receive mating recesses in a composite wing substructure so thatinterdigitation of the wing skin structure and support substructureresults. The interdigitating members are hollow so that a plurality oftransversely positioned triple wedges may be slid through theinterdigitating members which experience independent horizontal andvertical expansion from the wedges thereby locking the members togetherand strongly resisting delamination which often occurs along a planebetween the wing skin structure and the support substructure ofconventional assemblies.

Further advantages of the present invention relate to automated precutmaterial use which lends itself to rapid repeatable production andreduction of layup time. The tooling required is relativelyuncomplicated, which serves as a distinctive economic advantage of theinvention.

BRIEF DESCRIPTION OF THE FIGURES

The above-mentioned objects and advantages of the present invention willbe more clearly understood when considered in conjunction with theaccompanying drawings, in which:

FIG. 1 is a perspective view illustrating interlocking engagementbetween a wing skin structure and support substructure in accordancewith the present invention;

FIG. 2 is a disassembled view of top and bottom ply members constitutingan elementary wing skin structure;

FIG. 3 is a disassembled view of a wing skin structure and supportsubstructure in accordance with the present invention;

FIG. 4 is a perspective view of the triple wedge and receptacle lockingmeans as employed in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made to FIG. 1 wherein interlocking engagement between awing skin structure and support substructure is illustrated in a mannersimilar to that of my co-pending application Ser. No. 306,199, filedAug. 29, 1989, now U.S. Pat. No. 4,909,659. The interlocking members aregenerally indicated by reference numeral 10 and are seen to include awing support substructure 12 secured to a wing skin structure 14. Inorder to achieve the interlocking engagement between members 12 and 14,hollowed projections 16 are formed in the wing skin structure 14 and forillustrative purposes are indicated as two parallel spaced rowsextending longitudinally. A greater number of rows could, of course, bepresent. The wing support substructure 12 has, along a triangular baseportion, slots 13 formed therein so that the spacing between therecesses is the same as the spacing between longitudinally extendingadjacent projections. The slots 13 receive corresponding projections 16so that the engaging portions form interdigitations. The triangular baseportion of the substructure 12 and the projections 16 are hollowed sothat a transversely positioned wedge assembly 20 can slide throughtransversely aligned projections to secure interlocking engagementbetween the substructure 12 and the projections 16. Single wedgesecurement is disclosed in my copending application Ser. No. 131,699,filed Dec. 11, 1987, now U.S. Pat. No. 4,904,109, and utilization of adouble wedge assembly is disclosed in my copending application Ser. No.306,196, filed Feb. 6, 1989, now U.S. Pat. No. 4,892,435, issued Jan. 9,1990. The particular improvement of the present invention relates toadditional advantages of a novel triple wedge which is discussed ingreater detail in connection with FIG. 4. If the wing skin structure 14and the wing support substructure 12 were connected in conventionalfashion by rivets, a delamination plane would exist at the interfacebetween wing skin structure and support substructure, as indicated byreference numeral 22. When rivet construction is used, a danger existsthat sufficient stress upon the wing skin structure will delaminate orseparate the wing skin structure 14 from the wing support substructure12. The transverse orientation of the wedges 20 along the longitudinalinterface between wing skin structure 14 and wing support substructure12 greatly increases an aircraft's ability to resist delamination.

It is to be noted that the wing support substructure 12 is shown mountedin longitudinal offset relationship to the wing skin structure 14 sothat details of the invention are better illustrated. In actualutilization of the invention, the substructure 12 would be shifted tomore completely overlie the wing skin structure 14.

In order to better appreciate the construction of the present invention,reference is made to FIG. 2 wherein a top ply for the wing skinstructure is generally indicated by reference numeral 24. The ply may befabricated from a Fiberglass sheet 26 or from a number of conventionalcomposite materials. For simplicity of explaining the invention, onlysix spaced openings 28 are illustrated. These openings appear as twoparallel rows, the rows having a series of transversely aligned openingpairs of rectangular shape. A bottom ply 30 is fabricated from a sheet32 of appropriate material such as Fiberglass or selected compositematerial. The sheet 32 is interrupted by parallel spaced longitudinalmedial openings 34 bridged by integrally formed connecting projectionpairs 16 spaced to be in registry with corresponding openings 28.

By lowering the top ply 24 over the bottom ply 30 so that projections 16respectively project upwardly through corresponding openings 28, the twoplies become geometrically locked, as indicated by the completed wingskin structure 14 in FIG. 3. As is the case in existing compositeaircraft laminated structures, the individual plies are impregnated withresin and cured. Conventional pre-impregnated resins may be successfullyused in accordance with known practices.

It should be observed that FIGS. 2 and 3 illustrate the wing skinstructure as being fabricated from a single top and bottom layer.However, this has been done to simplify the explanation of theinvention. In order to achieve desired structural strength, it isanticipated that several sets of top and bottom layers will benecessary. Accordingly, FIG. 1 has been illustrated for an example wheretwo sets of top and bottom plies have been employed.

If the wing skin is desired to be of uniform thickness, strips 35 arepositioned in the medial openings 34, as indicated in FIGS. 1 and 3.

The final construction of the invention will now be explained inconnection with FIG. 3. The wing support substructure 12 is shown asfabricated from two plies of resin-impregnated fabric which, like thewing skin structure, may be made of Fiberglass or other suitablecomposite, the layers being folded over one another to form the flatportion 38. The lower portion of the wing support structure is formed asa closed, hollowed triangular portion, indicated by reference numeral 36which includes a base section 40.

In order to fabricate the composite wing skin structure and compositewing support substructure as rigid load-supportable members, the resinimpregnation of the composite fabrics must be cured. In this regard thewing skin structure 14 is cured separately from the support substructure12 and then they are assembled. A triple wedge 20 is passed through eachrespective projection 16 to lock the wing skin structure and supportsubstructure together.

In order to increase the substructure's resistance to shear forces, astrip of material (not shown) may be laced through the flat portion 38in a manner detailed in my co-pending U.S. patent application Ser. No.53,199, filed May 22, 1987, now U.S. Pat. No. 4,813,202, issued Mar. 31,1989.

The utilization of transverse locking means for securing composite wingskin structure and support substructure is disclosed in my previouslymentioned co-pending U.S. patent application Ser. No. 306,199, filedAug. 29, 1989, now U.S. Pat. No. 4,909,659. The thrust of the presentinvention is the utilization of a triple wedge assembly in combinationwith an expandable receptacle for achieving the transverse locking ofwing skin to support substructure. In my last-mentioned co-pendingapplication, the wing skin and support substructure are held together bya simple trapezoidal locking bar which slides through projections 16,which are likewise formed in a trapezoidal cross section. Theutilization of a simple locking bar is particularly appropriate wherethe wing skin and support substructure (both resin-impregnated) areco-cured. When this is accomplished, the bonding between the wing skinand support substructure is significant and the locking bar providesadditional securement.

However, the present invention is intended for applications where thewing skin structure and support substructure are intended to beseparately cured and, therefore, the locking of these structurestogether must rely totally upon triple wedges 20. The advantage of thepresent locking arrangement is that the wing skin structure and supportsubstructure may be separately fabricated and assembled later on.Likewise, it is possible to remove the wedges 20 and disassemble thewing skin structure from the support substructure if this becomesnecessary.

Referring back to FIG. 1 it will be seen that each pair of alignedtransverse projections 16 receives a parallelepiped-shaped receptacle50. The triple wedges 20 are actually force fitted into the oppositeends of the receptacle to expand the receptacle walls into engagementwith the projections 16, thereby locking the wing skin structure 14 tothe support substructure 12.

In greater detail, FIG. 4 indicates that the receptacle 50 ischaracterized by two opposite end sections 55 and 59 and a centralsection 57. The end section 55 includes slotted edges 56, 58, 60 and 62to allow vertical and horizontal expansion of the receptacle walls,outwardly, after insertion of the triple wedges 20. The central section57 includes no such slotted edges. Like section 55, the end section 59includes slotted edges 64, 66, and 68 as well as a fourth remainingslotted edge, hidden from view.

The triple wedge 20 includes a single centrally disposed wedge 71 forvertical expansion and which is preferably fabricated from a solid bodyand includes a parallelepiped section 70 extending to a tapered section72. The tapered section 72 includes an inclined upper surface 74 and alower inclined surface 76 as well as side walls 78 and 80. The upper andlower surfaces 74 and 76 include ridges 82 to engage correspondingridged surfaces 84 on interior upper and lower walls of end sections 55and 59 of receptacle 50.

Wedge 71 performs only vertical expansion (88) of the receptacle 50 whenit is initially driven (86) into the receptacle. Of course, the harderthe wedge 71 is driven into the receptacle 50, the greater the verticalexpansion will be.

In order to effect independent horizontal expansion of the receptacle50, a pair of wedges 94 is driven in direction 96 into receptacleopening 103 alongside wedge 71. The degree of horizontal expansion ofreceptacle 50 is governed by the extent to which the wedges 94 aredriven into the receptacle opening 103. The wedges 94 include an outwardparallelepiped section 98 extending to a section 100 inclined slightlyto prevent vertical interference with opening 103 which would upset theindependent vertical expansion of receptacle 50 by wedge 71. Eachoutward sidewall 102 includes a rippled section 106 that becomes engagedby a mating rippled vertical wall 85 in wedge 71. It should be pointedout that rippled sections 106 are tapered inwardly so that aninterference fit between the rippled sections and wall 85 causeshorizontal expansion (90) of receptacle 50.

As previously mentioned, a similar triple wedge 20 is employed on theright illustrated end of the receptacle and its insertion causes thevertical and horizontal independent expansions of end section 59.

As will be appreciated from the above-discussed invention, a significantadvantage of the present invention is the capability of independentlycausing vertical expansion and horizontal expansion of the inventivefastener device. This is significant when compared with the prior artwhere material deformation may cause a greater expansion in one or theother direction to an undesirable and possibly material-damaging degree.

The advantage of the triple wedge assembly over the double wedgeassembly disclosed in my copending application Ser. No. 306,196, filedFeb. 6, 1989, now U.S. Pat. No. 4,892,435, issued Jan. 9, 1990 is theability of the wedges 94 to assume individual insertion depths into thereceptacle thereby obviating the necessity of perfectly symmetricalplacement of the horizontal wedges 94 and the vertical wedge 71. Thus,the triple wedge assembly of the present invention exhibits highertolerance for non-uniform offset centers for the wedges.

Referring to FIG. 1, in order to assemble a wing skin structure 14 to asupport substructure 12, receptacles 50 are inserted through each pairof transversely aligned projections 16 after substructure 12 and wingskin 14 are joined. The central section 57 is medially disposed in thespace 18 between each of the projection pairs while the end sections 55and 59 are received within corresponding projections 16. Each triplewedge 20 is driven into a corresponding end section in the directionindicated by reference numerals 86 and 96. Upon insertion of wedges 20,a corresponding end section will vertically expand (88) and horizontallyexpand (90). A press fit will therefore result between the receptacle 50and each pair of corresponding retaining projections 16. After thetriple wedges 20 have been inserted, the wing skin structure 14 issecurely fastened to the support substructure 12. However, ifdisassembly of the wing skin structure from the support structurebecomes necessary, the wedges 20 may be pulled from the receptacles 50.In order to expedite such removal, bores 99 may be formed in wedges 94to permit the insertion of a pulling tool (not shown). A similar bore 92is formed in wedge 71 for the same purpose. By utilizing triple wedges20, close tolerance fits are achieved between the wing skin structureand support substructure so that minute sliding therebetween isinhibited. As a result, deformation of the mating parts is minimized.The close fit tolerance also avoids fastener bending which is notuncommon in high speed aircraft utilizing rivet construction. It shouldbe further noted that the large rectangular interface area between thebase of the support substructure 14 and wing skin 12 resists buckling ascompared to joints where rivets or the like are used.

In a finally assembled aircraft, the wing support substructure 12 andprojections 16 are positioned internally of the wing. The underside ofthe wing skin structure 14, opposite the surface illustrated, will formthe exterior surface of the wing skin. The utilization of transverselocking means, namely the triple wedges 20 within projections 16, offersthe capability of securely fastening the wing support 12 to the wingskin 14 even in the event that the wing skin 14 should have a contour,such as indicated by 44, instead of the planar appearance as indicatedin FIG. 1. A further distinctive advantage of the transversely locatedlocking means is the fact that rotational (hinge) rotation of the wingskin 14, relative to the wing support 12, is minimized.

Although the present invention has been explained in connection withprojections 16 of rectangular cross section and a triangular-based wingsupport substructure 12, this has been done to simplify the explanationand is only illustrative. Other mating shapes may be similarly employed.

As will be appreciated by virtue of the connection of wing skinstructure 14 to wing support substructure 12, without the aid of rivets,high stress points and leakage points between the two structures areeliminated.

Although the present invention has been described in terms of afastenerless joint for securing an aircraft wing skin to a supportstructure, it should be appreciated that the invention contemplatesother applications. Thus, the following claims envision generalutilization of projections from a first laminated structure to forminterdigitations with a support substructure to achieve a secure jointtherebetween. Specifically, the present invention is envisioned forapplications to securing other aircraft skin sections to supportsubstructures, in addition to a wing skin as discussed herein.

It should be understood that the invention is not limited to the exactdetails of construction shown and described herein, for obviousmodifications will occur to persons skilled in the art.

I claim:
 1. An expansion fastener comprising:a hollow receptaclehavinga) a first hollow section including a continuous wall, and b) atleast one additional hollowed section integrally extending coaxiallyfrom the first section and having slits formed in the wall thereof; anda triple interlocking wedge received within the slitted section forexpanding the slitted wall thereof, the triple wedge including a firstcentral wedge member havinga) at least one tapered surface forcontacting a mating tapered surface within the wall of the slittedsection, b) the tapered surface being ridged for engaging a mating ridgesurface within the wall of the slitted section; two wedge membersadapted to be driven into the slitted section alongside the centralfirst wedge member, each of the latter wedge members having an inwardlytapering rippled sidewall adapted to securely engage a mating rippledsurface formed i the wall of the slitted section; the driving insertionof the first central wedge member resulting in independent expansion ofthe receptacle in a first direction, and further wherein the drivinginsertion of the latter two wedge members into the receptacle results inindependent expansion of the receptacle in a second direction orthogonalto the first direction.
 2. The structure set forth in claim 1 togetherwith still another slitted section similar to the first and integrallyextending coaxially from the first continuous section in a directionopposite that of the first slitted section for receiving another triplewedge.
 3. The structure set forth in claim 1 wherein the central wedgemember has opposite ridged surfaces for engaging mating ridged surfacesin the wall of the slitted section.
 4. The structure set forth in claim1 wherein the height of the two wedge members is less than that of thecentral wedge member thereby preventing interfering contact between thetwo wedge members and the receptacle in the first direction.
 5. Anexpansion fastener comprising:a hollow receptacle havinga) a firstsection including a continuous wall, and b) at least one additionalhollowed section integrally extending coaxially from the first sectionand having slits formed in the wall thereof; and a triple interlockingwedge received within the slitted section for expanding the slitted wallthereof, the triple wedge including a first central wedge memberhavinga) tapered surfaces for contacting mating tapered surfaces withinthe wall of the slitted section, b) at least one tapered surface beingridged for engaging a mating ridged surface within the wall of theslitted section; two wedge members adapted to be driven into the slittedsection alongside the central first wedge member, each of the latterwedge members having an inwardly tapering rippled sidewall adapted tosecurely engage a mating rippled surface formed in the wall of theslitted section; the driving insertion of the first central wedge memberresulting in independent expansion of the receptacle in a firstdirection, and further wherein the driving insertion of the latter wedgemembers into the receptacle results in independent expansion of thereceptacle in a second direction orthogonal to the first direction; thereceptacle further including still another slitted section similar tothe first and integrally extending coaxially from the first continuoussection in a direction opposite that of the first slitted section forreceiving another triple wedge.
 6. The expansion fastener set forth inclaim 5 together with a first structural member having at least one pairof aligned hollow projections;a second hollowed structural member seatedagainst the first structural member in the space between projections;the expansion receptacle inserted through the projections and thehollowed structural member for locking them together; the triple wedgeexpanding the receptacle for securing the first and second structuralmembers together.
 7. The structure set forth in claim 6 wherein thefirst structural member is an aircraft skin structure and the secondstructural member is a support substructure, removal of the triple wedgefrom the receptacle permitting disassembly of the skin structure fromthe support substructure.
 8. A method for expanding a receptacle of afastener comprising:driving a first central wedge into an open slittedend of the receptacle which has an internal rippled surface, the wedgehaving a substantially mating rippled surface tapered in a firstdirection for limiting receptacle expansion in the first direction andfor engaging the mating rippled surface and securing the first wedge inthe receptacle; driving two additional wedges into the receptaclelaterally alongside the central wedge, the additional wedges and theslitted end having substantially mating rippled surfaces tapered in asecond orthogonal direction for independently limiting receptacleexpansion in the second direction and for securing the two additionalwedges in the receptacle.